Don't allow UMO to shrink to 1/3 size.

The current UMO really only supports two sizes: full-size and half-size.
Anything smaller causes controls within the UMO to overlap.

Bug: 360756056
Test: atest CommunalInteractorTest
Test: atest CommunalViewModelTest
Flag: EXEMPT bugfix

Change-Id: Ia0e39b16cfa0b1eccabcb87d9f11fc4df170621b